A126716 Least i such that prime(i)*2^(10^n) -1 is prime.

2, 3, 51, 657, 6255

Offset

0,1

Links

Table of n, a(n) for n=0..4.

Example

3*2^(10^0)-1=5 prime so a(0)=2 since 3 is prime(2).
3*2^(10^1)-1=3071=37*83 composite, 5*2^(10^1)-1=5119 prime so a(1)=3, since 5 is prime(3).

Prog

(PARI) a(n) = my(i=2); while (!isprime(prime(i)*2^(10^n) -1), i++); i; \\ Michel Marcus, Sep 15 2019

Crossrefs

Sequence in context: A065646 A268251 A090508 * A355648 A347894 A362836

Adjacent sequences: A126713 A126714 A126715 * A126717 A126718 A126719

Keyword

nonn,more

Author

Pierre CAMI, Feb 13 2007

Status

approved